This invention relates to luminaires and more particularly to devices and methods for mounting a lamp ballast on a luminaire.
Ballasts are normally utilized in luminaires of various types, such as high intensity sodium and mercury vapor lamps, as transformers, to step up the available line voltage to a level sufficient to properly energize the lamp. The ballasts are formed by a number of identical flat plates of generally rectangular shape composed of a meterial of good magnetic permeability, such as soft iron, and have primary and secondary coils of electrically conductive wire mounted therein. The plates are laminated together and provide the magnetic core for the ballast windings.
The lamp ballasts which are supplied by ballast manufacturers to lighting fixture manufacturers, who assemble and mount the ballasts and the other necessary components together in a lighting fixture, are manufactured with a plurality of holes therein, typically four or more. These holes are normally about 0.2 inch in diameter and pass through the core from one side to the other perpendicular to the plane of the laminated plates. The holes are formed by the ballast manufacturer by drilling or punching through the core plates at predetermined points adjacent the core periphery and are provided to permit the lighting fixture manufacturer to pass mounting bolts or shafts through the core. For a given ballast wattage, the length of the laminated core and hence, the transverse spacing between these bolt holes, is normally the same. However, the widths of cores having the same nominal wattage but different voltage and resistance parameters required for different types of lamps, are usually different. The ends of the mounting bolts are designed to be attached to a mounting plate by a pair of right angle mounting brackets.
The mounting brackets are elongated steel elements having two legs joined at right angles. One leg of each bracket is designed to be mounted flat against one of the core side plates and the other leg is designed to be mounted flat against an adjoining section of the mounting plate. The mounting bolts are passed through holes formed in the one leg of a first bracket concentric with the holes in the core and thence, through concentric holes formed in the one leg of a second bracket abutting an opposite side plate. The threaded ends of the bolts projecting from the bracket are captured by nuts. The other leg of each bracket is anchored to the mounting plate by screws which pass through holes formed in the other leg of each bracket and enter concentric tapped holes or apertures provided by the fixture manufacturer in underlying portions of the mounting plate.
As mentioned above, the width dimensions of ballasts supplied by various ballast manufacturers may vary for a given ballast wattage even though the length dimensions remain the same. Further, different ballast wattages normally require ballasts having both different length and width dimensions which means that the transverse spacings between and the lengths of the bolts hole will be different for each different ballast wattage. Using the aforedescribed conventional brackets, the replacement of a first ballast by a second ballast of different size but of the same nominal wattage presents the installer or the lighting fixture manufacturer with the problem of moving one of the two mounting brackets to a position inwardly or outwardly of its previous position in order to abut the ballast side plate and then remounting the bracket to the underlying mounting plate. Bracket relocating is especially troublesome for an installer who may be required to replace the ballast in situ in a lighting fixture which has not been provided with additional, properly located, tapped holes or apertures in the mounting plate. If the second ballast is of a different nominal wattage than the first ballast, then the transverse spacings between the bolt holes in the second ballast core will also be different and therefore, will not be in alignment with the bolt holes provided in the brackets for mounting the first ballast. In this case, two or more holes concentric with the bolt holes in the second ballast will now have to be drilled or punched through one leg of each bracket by the installer.
Moreover, since the bolts which pass through the cores and are captured by nuts at their ends may be of an appropriate length for the ballast core of smaller width; the mounting bolts could be too short to pass sufficiently far through a ballast core of greater width. On the other hand, the mounting bolts may prove to be too long. This is so because Underwriters Laboratory requires that the total length of the fully exposed threaded end projecting from the nut capturing the bolt or lug not exceed 3/16 of an inch. The purpose of this requirement is to ensure that the exposed threads do not extend far enough from the bracket to contact and abrade through the insulation of the luminaire's lead wires which may be near those threads. If the second ballast has a laminated core of smaller width than the first ballast but the same mounting bolts are used, to comply with these requirements it is necessary for the installer to provide suitable protective capping of the additional length of free thread ends now available through use of the thinner second ballast. Hence, to affect an approved replacement of the ballast may require that the installer and the fixture manufacturer maintain an inventory of mounting bolts of different lengths for possible use with ballasts of different widths or an inventory of a suitable type of protective thread cap.
The aforementioned problems resulting from the conventional use of brackets to mount lamp ballasts on luminaires is overcome by the instant invention.